1. Field of the Invention
This invention relates to a specific subset of the field of orthopedic surgery, namely, to devices and methods for the repair of pronounced bunion deformities, scientifically known as hallux valgus.
Hallux valgus is a deformity of the forefoot involving multiple components. It has been described as "static subluxation of the first metatarsophalangeal joint with lateral deviation of the great toe and medial deviation of the first metatarsal. It is occasionally accompanied by rotation or pronation of the great toe in severe cases." See Mann (Ed.), Surgery of the Foot 65 (5th ed. 1986).
One of the common causes of hallux valgus is prolonged deformation of the foot inside so-called high fashion shoes commonly worn by women. In such shoes, the great toe sits in an abnormal orientation for a long period of time, which eventually stretches out the joint capsule, in turn promoting migration of the muscles into an abnormal position. Thus, women have bunions many times more commonly than men do. Other factors which predispose patients to hallux valgus are rounded unstable metatarsophalangeal joint surfaces and oblique joint surfaces at the proximal first metatarsal joint.
In the production of hallux valgus deformity, a point is reached in which the muscles migrate laterally outside the joint line. Once this stage has been reached, the deformity is self-feeding and becomes inevitably worse.
The severity of hallux valgus deformities has traditionally been quantified in a variety of ways based on measurements from x-ray pictures. The first of the two most common measurement or quantification techniques for hallux valgus is the so-called IM or intermetatarsal angle between the line of the first and second metatarsal shafts. This angle is normally about six degrees; the upper limit of normal is about nine degrees. The second measurement is the hallux valgus angle, which is the angle between the first metatarsal shaft and the proximal phalanx. This would normally be about nine or ten degrees maximum. A measurement of 12 degrees would be almost uniformly regarded as abnormal. A typical hallux valgus patient might have an IM angle of 15 degrees and a hallux valgus ("HV") of 35 degrees.
2. Description of the Prior Art
Historically, many different procedures have been proposed to correct hallux valgus deformities. One such technique is the simple exostectomy, which is merely an excision of the prominent medial eminence of the first metatarsal head. This technique has limited usefulness. Kotzenberg in Germany, roughly a hundred years ago, described a side (medial) entry and proximal V-cut or chevron osteotomy repair of hallux valgus. In the early part of the 20th century, an operation was reported in which the exostosis of the medial eminence bone was used as a bone graft with a proximal opening wedge osteotomy. McNabb and Bonney at the National Orthopedic Hospital in London described a procedure in the 1940's including an opening wedge proximal osteotomy and graft with cross-metatarsal screw fixation.
Today, there are two groups of operations which are commonly done to correct hallux valgus and associated deformities. Review of the literature and surgical experience indicate that a five-degree correction of the intermetatarsal angle and a maximum of ten-degree correction of the hallux valgus is reproducibly possible with distal osteotomy procedures of which the commonly used ones have been the Mitchell and more recently the distal chevron osteotomy.
The second currently common operation for correction is the Roger Mann proximal osteotomy of the metatarsal shaft. The Mann technique is used for somewhat more severe bunionectomies and involves a soft tissue release distally in which the intermetatarsal ligament, the adductor hallucis and the capsule of the metatarsal phalangeal joint on its fibular side are cut. Then the osteotomy is done proximally permitting correction to be obtained. The two segments of the displaced first metatarsal shaft are fixed to each other with a pin inserted at an oblique angle. Presently, Mann employs a simple orthopedic threaded screw between the segments of the first metatarsal shaft, instead of the pin. The Mann osteotomy necessitates a certain incidence of nerve injury; at least 10 percent numb toes typically result.
The choice of repair from among the prior art procedures is to some degree guided by the IM and HV angles preoperatively. However, the surgical techniques described above are of questionable suitability for repairs of the more severe cases as the corrections are borderline in such instances. For example, given a preoperative IM angle of 15 and an HV angle of 30, a distal procedure is barely going to correct that down into the normal range. Likewise, in the more severe cases, the Mann distal soft tissue procedure with proximal osteotomy does not always produce a satisfactory correction of the deformity. Malunion and non-union have also been recorded for both types of repairs.
Turning to the patent literature, U.S. Pat. No. 4,159,716 to Borchers describes a clamp apparatus and method for compressing and realigning bone structures to correct splay foot. U.S. Pat. No. 3,809,075 to Matles teaches wire or pin bone splints having at least one unitary hinged retainer of soft bendable material with wings adapted to detachably secure the member to a selected location on the wire or pin. U.S. Pat. No. 4,969,909 to Barouk describes a bent ended pin for longitudinal insertion into the medullary canals of a digit with a cup shaped adaptation at the articulation position between two bones. Toe prostheses useful at the metatarsal/phalangeal joint are fairly widely described in the patent literature, but offer little guidance in the, repair of hallux valgus. See U.S. Pat. Nos. 4,908,031 to Fisch; 4,787,908 to Wyss; 4,731,087 to Sculco et al.; 4,642,122 to Steffee; and 4,156,296 to Johnson et al.